The present invention relates to multi-phase detergent tablets. In particular, it relates to multi-phase detergent tablets having improved robustness and product integrity together with excellent dissolution characteristics. The invention also relates to methods of manufacturing multi-phase detergent tablets and to detergent auxiliary compositions useful therein.
Detergent compositions in tablet form are known in the art. It is understood that detergent compositions in tablet form hold several advantages over detergent compositions in particulate form, such as ease of dosing, handling, transportation and storage.
Detergent tablets are most commonly prepared by pre-mixing components of a detergent composition and forming the pre-mixed detergent components into a tablet using any suitable equipment, preferably a tablet press. Tablets are typically formed by compression of the components of the detergent composition so that the tablets produced are sufficiently robust to be able to withstand handling and transportation without sustaining damage. In addition to being robust, tablets must also dissolve sufficiently fast so that the detergent components are released into the wash water as soon as possible at the beginning of the wash cycle.
However, a dichotomy exists in that as compression force is increased, the rate of dissolution of the tablets becomes slower. The present invention therefore seeks to find a balance between tablet robustness and tablet dissolution.
Solutions to this problem, as seen in the prior art, have included compressing the tablets with low compression pressure. However tablets made in this way, although having a fast relative dissolution rate, tend to crumble, becoming damaged and unacceptable to the consumer. Other solutions have included preparing tablets using a high relative compression pressure, in order to achieve the required level of robustness, and comprising a dissolution aid, such as an effervescent agent.
Multi-phase detergent tablets described in the prior art are prepared by compressing a first composition in a tablet press to form a substantially planar first layer. A further detergent composition is then delivered to the tablet press on top of the first layer. This second composition is then compressed to form another substantially planar second layer. Thus the first layer is generally subjected to more than one compression as it is also compressed during the compression of the second composition. Typically the first and second compression forces are in the same order of magnitude. The Applicant has found that where this is the case, because the compression force must be sufficient to bind the first and second compositions together, the force used in both the first and second compression steps must be in the range of from about 4,000 to about 20,000 kg (assuming a tablet cross-section of about 10 cm2). A consequence of this is a slower rate of tablet dissolution. Other multi-phase tablets exhibiting differential dissolution are prepared such that the second layer is compressed at a lower force than the first layer. However, although the dissolution rate of the second layer is improved, the second layer is soft in comparison to the first layer and is therefore vulnerable to damage caused by handling and transportation. Moreover, the two layers are found to have poor adhesion characteristics and can break up under the relatively mild stress conditions found in storage or transportation.
The present invention therefore provides multi-phase detergent tablets for use in automatic dishwashing, laundry, etc and which have improved integrity and robustness together with excellent dissolution characteristics. The invention also provides methods of manufacturing multi-phase detergent tablets and detergent auxiliary compositions useful therein.
According to a first aspect of the invention, there is provided a multi-phase detergent tablet for use in a washing machine, the tablet comprising a first phase in adhesive contact with one or more second phases, and wherein at least the first phase is in the form of a compressed particulate solid incorporating a cogranulated detergency additive composition comprising polymeric polycarboxylate and inorganic carrier.
The compositions of the invention thus comprise multiple phases in adhesive contact with one another, at least a first phase of which is in the form of a compressed particulate solid incorporating cogranules of a detergency additive composition. In preferred embodiments, at least one and preferably each second phase is also in the form of a compressed particulate solid and, if desired, can also incorporate cogranules of the same or different detergency additive composition. Surprisingly, inclusion of the detergency additive composition in the first phase improves inter-phase adhesion at a given tablet compaction force (even where the second phase is free of cogranulated additive composition) and allows a significant reduction in compaction force on both first and second phases whilst delivering improved tablet solubility and bite strength.
A preferred cogranulated detergency additive composition for incorporation herein comprises i) from about 0.1% to about 60%, preferably from about 1% to about 25%, more preferably from about 5% to about 20% by weight thereof of polymeric polycarboxylate, ii) from about 40% to about 99.9%, preferably from about 70% to about 99%, more preferably from 80% to about 95% by weight thereof of inorganic carrier, and optionally iii) from 0% to about 50%, preferably from about 0.5% to about 20% by weight thereof of one or more organic auxiliaries, preferably selected from chelating agents, surfactants, polymeric disintegrants, solubility aids and mixtures thereof.
Polymeric polycarboxylates suitable for inclusion in the detergency additive composition include i) homo- and copolymers of one or more carboxylic monomers selected from acrylic acid, methacrylic acid, alpha-chloroacrylic acid, alpha-hydroxyacrylic acid, maleic acid, itaconic acid, and mixtures thereof, and ii) copolymers of one or more of the above carboxylic monomers with one or more nonionic monomers selected from acrylamide, acrylonitrile, vinyl esters such as vinyl acetate, methylvinyl ketone, acrolein, styrene and alpha-methyl styrene, alkyl vinyl ethers, esters and amides of carboxylic monomers such as (C1-C4)-alkyl (meth)acrylates, and water-soluble salts and mixtures thereof. Of the above, preferred are homo- and copolymers of acrylic and methacrylic acid
The polymeric polycarboxylates herein can be in acid, neutralised or partially neutralised form with sodium, potassium, ammonium or other counterions. Molecular weights of the polymeric polycarboxylates can vary widely e.g. weight averages ranging from about 500 to about 5,000,000, but normally weight average molecular weights will fall in the range from about 1000 to about 100,000. Preferably, the polymeric polycarboxylates will be in liquid or liquifiable form, for example as a solution, dispersion, slurry or emulsion in a liquid or liquifiable medium such as water or a water/organic solvent mixture. Generally, liquid or liquifiable polymeric polycarboxyate mixtures suitable for use herein have a polymer solids content of at least about 10%, preferably from about 20% to about 70%, more preferably from about 40% to about 60% by weight thereof.
The inorganic carrier herein generally comprises one or more inorganic salts and in preferred embodiments is selected from alkali metal silicate, alkali metal carbonate, alkali metal bicarbonate, alkali metal sesquicarbonate, alkali metal sulfate, alkali metal tripolyphosphate, and mixtures thereof. Of these, highly preferred is an inorganic carrier which comprises a mixture of alkali metal carbonate and alkali metal sulfate, preferably in a weight ratio of from about 3:1 to about 1:3, more preferably from about 2:1 to about 1:1, and especially from about 1.8:1 to about 1.5:1. The inorganic carrier normally takes the form of a powder or mixture of powders having a weight-average particle size of less than about 200 xcexcm preferably less than about 150 xcexcm, such carriers being preferred from the viewpoint of providing optimum granulometry, tablet strength, inter-phase adhesivity and solubility characteristics.
Thus according to another aspect of the invention, there is provided a cogranulated detergency additive composition comprising i) from about 0.1% to about 60%, preferably from about 1% to about 25%, more preferably from about 5% to about 20% by weight of polymeric polycarboxylate, ii) from about 40% to about 99.9%, preferably from about 70% to about 99%, more preferably from 80% to about 95% by weight of inorganic carrier in the form of a powder or mixture of powders having a weight-average particle size of less than about 200 xcexcm, preferably less than about 150 xcexcm, and optionally iii) from 0% to about 50%, preferably from about 0.5% to about 20% by weight of one or more organic auxiliaries selected from chelating agents, surfactants, polymeric disintegrants, solubility aids and mixtures thereof.
A preferred method for making the tablets herein comprises the step of admixing a liquid feed comprising the polymeric polycarboxylate with a powder feed comprising the inorganic carrier and subjecting the mixture to conditions of agitation and heat to form cogranules of the detergency additive composition. In a highly preferred embodiment, the liquid feed and powder feed are admixed under essentially non-evaporative conditions to form a wet cogranular output stream and the wet cogranular output stream is subsequently subjected to heat-drying, for example in a fluidised bed. In subsequent steps, the cogranules are compacted optionally with other detergent tablet ingredients to form the first phase of the tablet, the second phase is superposed in particulate or tablet form on or over the first phase and thereafter the first phase and superposed second phase are further compacted to form the final multi-phase detergent tablet.
Manufacture of the cogranular detergency additive composition is preferably undertaken in a vertical, short retention time, plow-type agglomerator such as a Schugi Flexomix followed by drying of the wet agglomerates in a fluidized bed dryer with fines recycling and size reduction as necessary to achieve the requisite granule size distribution. The liquid feed, ususally in the form of a solution, dispersion, slurry or emulsion of polymeric polycarboxylate in a liquid or liquifiable medium such as water or a water/organic solvent mixture, is preferably applied to the powder feed by spray-on at a slightly elevated temperature in order to provide an appropriate feed viscosity.
The powder feed, on the other hand, comprises inorganic carrier, preferably in the form of a powder or mixture of powders having a weight-average particle size of less than about 200 xcexcm, preferably less than about 150 xcexcm, together with any recycled fines. The liquid:powder feed ratio is generally less than about 0.5 preferably less than about 0.4, more preferably from about 0.1 to about 0.35, and especially from about 0.2 to about 0.3. In preferred embodiments, the powder feed comprises a mixture of alkali metal carbonate and alkali metal sulfate in a weight ratio of from about 3:1 to about 1:3, more preferably from about 2:1 to about 1:1, and especially from about 1.8:1 to about 1.5:1.
The process herein is highly preferred from the viewpoint of providing cogranular detergency additive compositions having the requisite granulometry for making compacted multi-phase detergent tablets of optimum strength, adhesion, and solubility characteristics.
Thus, according to further aspect of the invention there is provided a method of making a cogranular detergency additive composition comprising admixing a liquid feed comprising a polymeric polycarboxylate with a powder feed comprising inorganic carrier and subjecting the mixture to conditions of agitation and heat, and wherein the polymeric polycarboxylate is in the form of a solution, dispersion, slurry or emulsion in a liquid or liquifiable medium, the inorganic carrier is in the form of a powder or mixture of powders having a weight-average particle size of less than about 200 xcexcm preferably less than about 150 xcexcm, and wherein the liquid:powder feed ratio is less than about 0.5, preferably less than about 0.4, more preferably from about 0.1 to about 0.35, and especially from about 0.2 to about 0.3.
From the granulometry viewpoint, preferred cogranuar detergent additive compositions have an apparent density in the range from about 400 to about 1100 g/l, preferably from about 600 to about 900 g/l, a median granule size of from about 400 to about 700, preferably from about 450 to about 650 xcexcm, and a size distribution such that no more than about 5% by weight is greater than 1500 xcexcm, preferably 1400 xcexcm, and at least about 95% by weight is greater than 200 xcexcm, preferably 250 xcexcm. In addition, the cogranuar detergent additive compositions preferably have a final moisture content of less than about 5%, preferably from about 1% to about 3% by weight thereof. The cogranulated detergency additive composition generally comprises at least about 5%, preferably from about 10% to about 80%, more preferably from about 20% to about 60% by weight of the final tablet.
In compositional terms, a preferred cogranulated detergency additive composition for use herein i) from about 1% to about 25%, preferably from about 5% to about 20% by weight thereof of polymeric polycarboxylate, ii) from about 30% to about 85%, preferably from about 45% to about 65% by weight thereof of alkali metal carbonate, alkali metal bicarbonate, alkali metal sesquicarbonate or mixture thereof, and iii) from about 13% to about 69%, preferably from about 15% to about 50% by weight thereof of alkali metal sulfate, and optionally iv) from 0% to about 5% by weight thereof of organic chelating agent. Such a composition is highly suited for incorporation in so-called nil-P detergent tablets, i.e., tablets containing no phosphate builder and a minimal amount, if any, of phosphorus-containing chelating agents. Generally such tablets will contain phosphorus in an amount less than about 0.5%, preferably less than about 0.1% by weight.
Thus, according to a still further aspect of the invention, there is provided a cogranulated detergency additive composition comprising from about 5% to about 20% by weight of polymeric polycarboxylate and from about 80% to about 95% by weight of inorganic carrier, the inorganic carrier comprising i) from about 45% to about 65% by weight of the additive composition of alkali metal carbonate, alkali metal bicarbonate, alkali metal sesquicarbonate or mixture thereof, and ii) from about 15% to about 50% by weight of the additive composition of alkali metal sulfate.
Organic chelating agents suitable for inclusion in the cogranulated detergency additive composition or in the remainder of the tablet composition include diethylenetriamine penta (methylene phosphonate), ethylenediamine tetra(methylene phosphonate) hexamethylenediamine tetra(methylene phosphonate), ethylene diphosphonate, hydroxy-ethylene-1,1-diphosphonate, nitrilotriacetate, ethylenediaminotetracetate, ethylenediamine-N,Nxe2x80x2-disuccinate, methylglycinediacetic acid in their salt and free acid forms.
Polymeric disintegrants suitable for inclusion in the cogranulated detergency additive composition or in the remainder of the tablet composition include starch, cellulose and derivatives thereof, alginates, sugars, polyvinylpyrrolidones, swellable clays and mixtures thereof.
Solubility aids suitable for inclusion in the cogranulated detergency additive composition or in the remainder of the tablet composition include water-soluble hydrated salts having a solubility in distilled water of at least about 25 g/100 g at 25xc2x0 C., preferably selected from hydrates of sodium acetate, sodium potassium tartrate, sodium citrate and mixtures thereof.
The detergent tablets herein comprise at least one first phase in adhesive contact with one or more second phases (sometimes referred to herein as xe2x80x98optional subsequent phasesxe2x80x99). In preferred embodiments, the first phase is a compressed shaped body prepared at an applied compression pressure of at least about 40 kg/cm2, preferably at least about 250 kg/cm2, more preferably at least about 350 kg/cm2 (3.43 kN/cm2 or 34.3 MPa), even more preferably from about 400 to about 2000 kg/cm2, and especially from about 600 to about 1600 kg/cm2 (compression pressure herein is the applied force divided by the cross-sectional area of the tablet in a plane transverse to the applied forcexe2x80x94in effect, the transverse cross-sectional area of the die of the rotary press). The second phase, on the other hand, is preferably formed at a compression pressure of less than about 350 kg/cm2, preferably in the range from about 40 kg/cm2 to about 300 kg/cm2 and more preferably from about 70 to about 270 kg/cm2. In preferred embodiments, moreover, the first phase is formed by compression at a pressure greater than that applied to the second phase. In these embodiments, the compression pressures applied to the first and second phases will generally be in a ratio of at least about 1.2:1, preferably at least about 2:1, more preferably at least about 4:1.
Although simple multi-layer tablets are envisaged for use herein, preferred from the viewpoint of optimum product integrity, strength (measured for example by the Child Bite Strength [CBS] test) and dissolution characteristics are tablets wherein the first phase is in the formed of a shaped body having at least one mould therein; and the second phase is in the form of a particulate solid compressed within said mould. Such embodiments are sometimes referred to herein as xe2x80x98mouldxe2x80x99 embodiments. The tablets of the invention, both mould embodiments and otherwise, will preferably have a CBS of at least about 6 kg, preferably greater than about 8 kg, more preferably greater than about 10 kg, especially greater than about 12 kg, and more especially greater than about 14 kg, CBS being measured per the US Consumer Product Safety Commission Test Specification.
It is also preferred that the first and second phases herein are in a relatively high weight ratio to one another, for example at least about 6:1, preferably at least about 10:1; also that the tablet composition contain one or more detergent actives (for example enzymes, bleaches, bleach activators, bleach catalysts, surfactants, chelating agents etc) which is predominantly concentrated in the second phase, for example, at least about 50%, preferably at least about 60%, especially about 80% by weight of the active (based on the total weight of the active in tablet) is in the second phase of the tablet. Again, such compositions are optimum for tablet strength, dissolution, cleaning, and pH regulation characteristics providing, for example, tablet compositions capable of dissolving in the wash liquor so as to deliver at least 50%, preferably at least 60%, and more preferably at least 80% by weight of the detergent active to the wash liquor within 10, 5, 4 or even 3 minutes of the start of the wash process.